The survival rate, p, of a measured inoculum of Staph. aureus in a standard volume of denbrinated blood, is a reliable quantitative measure of the bactericidal power of blood. The number of viable organisms in the inoculum and in the blood-bacterium mixture may be estimated with the necessary accuracy by counts of colonies developing from measured volumes of the fluids let fall on to the surface of solid media. Fildes' agar was the most suitable medium for this surface-viable count, and was selected on the basis of four criteria; of the media tested it yielded the highest counts, and the counts conformed most closely to a Poisson series; and on it the mean colony size was maximum, and the coefficient of variation of colony size was minimum. On this medium, the close conformity of the separate count values to a Poisson series enabled the standard error of the survival rate to be determined from a simplification of the general expression for the standard error of a ratio.

The number of colonies growing from a sample of a blood-bacterium mixture may be reduced, not by killing of the individual cocci, but as a result of their aggregation either by agglutinins in the blood, or in the cytoplasm of leucocytes that are phagocytic but not bactericidal. It appears that these mechanisms are unlikely to operate in blood-bacterium mixture containing relatively few organisms; in such mixtures the survival rate is a reflexion of the killing power only.

The immunological significance of p has not been investigated, but the range of values for healthy human adults differs significantly from that for sufferers from chronic staphylococcal infection. Moreover, by the technique employed differences may be detected between individual values of p that cannot reasonably be attributed to technical or sampling errors.

1. In the course of the examination of sputum from cases of lobar pneumonia, observations have been made on the incidence of the chief types of pneumococci. In the district from which the material was obtained, there was an apparent local diminution in the number of cases of lobar pneumonia due to Type II the figures were 326 per cent. of Type II cases in the period 1920–22, and only 74 per cent. in the period 1924–27. The incidence of Type I was approximately the same in the two periods, the percentages being 3O6 and 343.

2. Several different serological varieties of pneumococci have been obtained from the sputum of each of several cases of pneumonia examined at various stages of the disease. This has occurred most frequently in cases of pneumonia due to Type I, and in two instances four different types of Group IV were found in addition to the chief types. The recovery of different types is facilitated by the inoculation of the sputum (preserved in the refrigerator), together with protective sera corresponding to the various types in the order of their appearance.

3. Two interesting strains of Group IV pneumococci have been obtained from pneumonic sputnm.

One was an R strain which produced typical rough colonies, yet preserved its virnlence for mice and its capacity to form soluble substance. This R pneumococcus developed a large capsnle in the mice, which died of a chronic type of septicaemia. A strain producing smooth colonies was obtained from it in the course of a prolonged series of passage experiments.

The second strain, which was proved not to be a mixture, agglutinated specifically with the sera of two different types. In the peritoneal cavity of the mouse the specific soluble substance of each type was produced.

4. A method of producing the S to R change through ageing of colonies on chocolate blood medium containing horse serum is described. After two to three days' incubation small rough patches appear in the margins of the smooth colonies, and from these pure R strains can be isolated.

5. It has been shown that the R change is not equally advanced in the descendants of virulent pneumococci which have been exposed to the action of homologous immune serum. Some R strains form traces of soluble substance in the peritoneal cavity of the mouse; these revert readily to the virulent S form and, in addition, are able to produce active immunity. Others show no evidence of S antigen; spontaneous reveraion takes place with difficulty, if at all, and they are incapable of producing active immunity. The stronger the immune serum used, the more permanent and complete is the change to the R form.

6. Restoration of virulence to an attenuated R strain, with recovery of the S form of colony and of the original serological type characters may be obtained by passage through mice. The change from the R to the S form is favoured by the inoculation of the R culture in large doses into the subcutaneous tissues; but the most certain method of procuring reversion is by the inoculation of the R culture, subcutaneously into a mouse, together with a large dose of virulent culture of the same type killed by heat. Incubation of such a mixture in vitro does not induce reversion.

7. Reversion of an R strain to its S form may occasionally be brought about by the simultaneous inoculation of virulent culture of another type, especially when this has been heated for only a short period to 60° 0., e.g. R Type II to its S form when inoculated with heated Type I culture.

8. Type I antigen appears to be more sensitive to exposure to heat than Type II antigen, since the former loses the power to cause reversion when heated to 80° C., whereas Type II culture remains effective even after steaming at 100°C.

9. The antigens of certain Group IV strains appear to be closely related to that of Type II, and are equally resistant to heat. Steamed cultures of these Group IV strains cause the R form derived from Type II to revert to its S form, while they fail to produce reversion of the R form derived from Type I.

10. The inoculation into the subcutaneous tissues of mice of an attenuated R strain derived from one type, together with a large dose of virulent culture of another type killed by heating to 60° C., has resulted in the formation of a virulent S pneumococcus of the same type as that of the heated culture.

Thp newly formed S strain may remain localised at the seat of inoculation, or it may disseminate and cause fatal septicaemia.

The S form of Type I has been produced from the R form of Type II, and the R form of Type I has been transformed into the S form of Type II.

The clear mucinous colonies of Type III have been derived both from the R form of Type I and from the R form of Type II, though they appear to be produced more readily from the latter. The newly formed strains of Type III have been of relatively low virulence, and have frequently remained localised at the subcutaneous seat of inoculation.

Virulent strains of Types I and TI have been obtained from an R strain of Group IV.

11. Heated R cultures injected in large doses, together with small doses of living R culture have never caused transformation of type, and only rarely produced a reversion of the R form of Type II to its virulent S form.

12. The results of the experiments on enhancement of virulence and on transformation of type are discussed and their significance in regard to questions of epidemiology is indicated.

In 1981, R. Edgar Hope-Simpson proposed that a ‘seasonal stimulus’ intimately associated with solar radiation explained the remarkable seasonality of epidemic influenza. Solar radiation triggers robust seasonal vitamin D production in the skin; vitamin D deficiency is common in the winter, and activated vitamin D, 1,25(OH)2D, a steroid hormone, has profound effects on human immunity. 1,25(OH)2D acts as an immune system modulator, preventing excessive expression of inflammatory cytokines and increasing the ‘oxidative burst’ potential of macrophages. Perhaps most importantly, it dramatically stimulates the expression of potent anti-microbial peptides, which exist in neutrophils, monocytes, natural killer cells, and in epithelial cells lining the respiratory tract where they play a major role in protecting the lung from infection. Volunteers inoculated with live attenuated influenza virus are more likely to develop fever and serological evidence of an immune response in the winter. Vitamin D deficiency predisposes children to respiratory infections. Ultraviolet radiation (either from artificial sources or from sunlight) reduces the incidence of viral respiratory infections, as does cod liver oil (which contains vitamin D). An interventional study showed that vitamin D reduces the incidence of respiratory infections in children. We conclude that vitamin D, or lack of it, may be Hope-Simpson's ‘seasonal stimulus’.

Foodborne outbreaks from contaminated fresh produce have been increasingly recognized in many parts of the world. This reflects a convergence of increasing consumption of fresh produce, changes in production and distribution, and a growing awareness of the problem on the part of public health officials. The complex biology of pathogen contamination and survival on plant materials is beginning to be explained. Adhesion of pathogens to surfaces and internalization of pathogens limits the usefulness of conventional processing and chemical sanitizing methods in preventing transmission from contaminated produce. Better methods of preventing contamination on the farm, or during packing or processing, or use of a terminal control such as irradiation could reduce the burden of disease transmission from fresh produce. Outbreak investigations represent important opportunities to evaluate contamination at the farm level and along the farm-to-fork continuum. More complete and timely environmental assessments of these events and more research into the biology and ecology of pathogen-produce interactions are needed to identify better prevention strategies.

The effect of oral administration of antibiotics on the intestinal flora of conventional mice and their resistance to colonization by orally introduced Escherichia coli, Klebsiella pneumoniae and Pseudomonas aeruginosa was studied. Colonization resistance (CR) was expressed as the log of the oral bacterial dose followed by a persistent take in 50 % of the contaminated animals. The intestinal flora was virtually eliminated by the antibiotics and this elimination was accompanied by a precipitous fall of CR. CR gradually returned to normal values during the period of repopulation of the intestinal tract by the organisms surviving the treatment. Antibiotic treatment resulted in the disappearance of Enterobacteriaceae, enterococci, staphylococci and yeasts and, under appropriate housing conditions, the animals remained free of these organisms indefinitely. Germ-free mice contaminated with the intestinal flora of an antibiotic-treated animal and their offspring housed in a germ-free isolator showed high values of CR. Their intestinal flora consisted of anaerobic bacteria only. Apparently, these anaerobes are responsible for CR in these and in conventional mice.

This study examines a cohort of persons quarantined during the 2003 SARS outbreak in Canada and describes their understanding of, difficulties and compliance with, and the psychological impact of the quarantine experience. A mailed questionnaire was administered to 1912 eligible adults and included the Impact of Events Scale – Revised (IES-R) to assess symptoms of post-traumatic stress disorder (PTSD). Self-reported compliance with all required quarantine measures was low (15·8±2·3%), although significantly higher when the rationale for quarantine was understood (P=0·018). Health-care workers (HCW) experienced greater psychological distress, including symptoms of PTSD (P<0·001). Increasing perceived difficulty with compliance, HCW, longer quarantine and compliance with quarantine requirements were significant contributors to higher IES-R scores. The low compliance with quarantine requirements introduces concerns about the effectiveness of quarantine as a public health measure. Improvements in compliance and reduced psychological distress may be possible by minimizing duration, revising requirements, and providing enhanced education and support.

The intranasal inoculation of volunteers with living partially attenuated strains of influenza A and B viruses offers a new opportunity to determine the protective effect of serum haemagglutin-inhibiting antibody against a strictly homologous virus, under conditions where the time and dosage of the infective challenge can be controlled, the scoring of proven infections can be more precise and higher rates of infection can be achieved than in most natural epidemics.

In 1032 adult volunteers, whose serum HI antibody titre was determined immediately before virus challenge, there was a consistent inverse quantitative relationship between the HI titre and the likelihood of infection. The PD50 (50 % protective dose) of HI antibody was 1/18–1/36, but an unusual finding was that volunteers with no detectable pre-challenge antibody often seem to be less susceptible to infection than those with pre-challenge antibody in low titre.

In one group of volunteers challenged with an influenza B strain there was no evidence that pre-challenge antibody titres against viral neuraminidase had any significant protective effect against challenge infection.

1. A very complete analogy exists between a chemical reaction and the process of disinfection, one reagent being represented by the disinfectant, and the second by the protoplasm of the bacterium.

2. Three classes of disinfectants were studied, (a) metallic salts (HgCl2 and AgNO3), (b) phenol, and (c) emulsified disinfectants (disinfectant “A”). B. paratyphosus and spores of B. anthracis were chosen as types of vegetative and spore-bearing organisms respectively.

3. In the case of anthrax spores, the disinfection process proceeds in obedience to the well-known equation for a unimolecular reaction, if numbers expressing “concentration of reacting substance” are replaced by “numbers of surviving bacteria”.

4. Experiments with B. paratyphosus show a departure from the simple law owing to permanent differences in resistance to disinfectants among the individual organisms. The younger bacteria were proved to be the more resistant.

5. The process of disinfection is influenced by temperature in an orderly manner, and the well-known equation of Arrhenius can be applied.

(a) Disinfection of B. paratyphosus by metallic salts is influenced by temperature to about the same degree as most chemical reactions, the reaction velocity being increased about three-fold for a rise in temperature of 10°C.

(b) For disinfection of B. paratyphosus by phenol and the disinfectant “A” there was a much higher temperature coefficient, viz., seven to eight. In the case of phenol the effect of temperature was again found to be complicated by the want of uniformity among the individual bacteria. Disinfection of the younger, more resistant bacteria, was found to possess a higher temperature coefficient than that of the less resistant forms, the coefficient varying from ten to three, or two according to the age and number of the bacteria disinfected.

6. It follows from (5) that there is a very great advantage in the use of warm solutions for practical disinfection.

7. Experiments, made with varying concentrations of disinfectant, and using similar groups of bacteria from cultures of B. paratyphosus, showed a definite logarithmic relation, between the concentration of disinfectant and the mean reaction velocity of disinfection, to exist in the case of phenol and the disinfectant “A”.

8. In the case of silver nitrate, the same relation existed, but, in the case of mercuric chloride, numbers representing concentration of the salt had to be replaced by those representing concentration of the metallic ion. This confirms the theory that in disinfection with metallic salts the metallic ion is the real disinfecting agent.

9. This logarithmic relation is surprising in view of the simple proportionality existing in the case of chemical processes running the course of a unimolecular reaction, with which disinfection shows a close analogy.

10. Some evidence was obtained that, in disinfection with mercuric chloride, a toxic compound is formed between the metal and the substance of the bacterial cell. This compound prevents all further growth, but vitality can be restored by the administration of a large excess of soluble sulphide as an antidote.

I am glad to have this opportunity of expressing my great indebtedness to Dr C. J. Martin, at whose suggestion the work was undertaken, and who has helped me throughout, not only with most valuable advice, but also with practical assistance in many of the experiments.

1. The sizes of the droplets and droplet-nuclei produced by sneezing, by coughing and by speaking, were studied by the microscopic measurement of 12,000 droplet stain-marks found on slides exposed directly to mouth-spray, and of 21,000 stain-containing droplet-nuclei recovered from the air on to oiled slides exposed in the slit sampler.

2. From these measurements it was calculated that the original diameters of the respiratory droplets ranged from 1 to 2000 μ, that 95 % were between 2 and 100 μ and that the most common were between 4 and 8 μ. Similar size distributions were exhibited by the droplets produced in sneezing, in coughing and in speaking, except that, in the case of sneezing, the smaller droplets were relatively more numerous.

3. The respiratory droplet-nuclei were found to range in diameter from ¼ to 42 μ; 97 % had diameters between ½ and 12μ; the commonest diameter was between 1 and 2 μ.

4. The proportion of droplets of each size which will contain bacteria, whether commensal or pathogenic, is determined by the size of the droplets and by the numbers of bacteria in the secretions atomized. Calculations made on the basis of the size distributions obtained in this investigation indicated that few of the smaller droplets, and thus few of the droplet-nuclei, are likely to contain pathogenic organisms. Droplet-spray is unlikely to give rise directly to true airborne infection unless very large numbers of pathogenic organisms are present in the secretions of the anterior mouth.

5. The persistence of droplet-nuclei in the air of a 1700 cu.ft. room and of a 70 cu.ft. chamber was investigated by sampling the air with the slit sampler at intervals following sneezing.

6. When the air was not artificially disturbed by a fan, the time taken for the disappearance from the air of 90% of the bacteria-carrying droplet-nuclei varied from 30 to 60 min.; the nuclei larger than 8 μ in diameter usually disappeared within 20 min., and the nuclei larger than 4 μ within 90 min.; the smaller nuclei, few of which contained bacteria, remained airborne for much longer periods, on one occasion for at least 30 hr. When a fan was run throughout the experiment, the nuclei disappeared from the air much more rapidly.

After preliminary trials, the detailed changes in the concentration of specific circulating and local antibodies were followed in 15 volunteers inoculated with coronavirus 229E. Ten of them, who had significantly lower concentrations of pre-existing antibody than the rest, became infected and eight of these developed colds. A limited investigation of circulating lymphocyte populations showed some lymphocytopenia in infected volunteers. In this group, antibody concentrations started to increase 1 week after inoculation and reached a maximum about 1 week later. Thereafter antibody titres slowly declined. Although concentrations were still slightly raised 1 year later, this did not always prevent reinfection when volunteers were then challenged with the homologous virus. However, the period of virus shedding was shorter than before and none developed a cold. All of the uninfected group were infected on re-challenge although they also appeared to show some resistance to disease and in the extent of infection. These results are discussed with reference to natural infections with coronavirus and with other infections, such as rhinovirus infections.

Over the past 5 years Salmonella enteritidis infections in humans have increased on both sides of the Atlantic ocean. The WHO salmonella surveillance data for 1979–87 were reviewed and show that S. enteritidis appears to be increasing on at least the continents of North America, South America, and Europe, and may include Africa. S. enteritidis isolates increased in 24 (69%) of 35 countries between 1979 and 1987. In 1979, only 2 (10%) of 21 countries with reported data reported S. enteritidis as their most common salmonella serotype; in 1987, 9 (43%) of 21 countries reported S. enteritidis as their most common serotype; 8 (89 %) of 9 were European countries. Although the reason for the global increase is not yet clear, investigations in individual countries suggest it is related to consumption of eggs and poultry which harbour the organism.

This report on a large outbreak of disease, known locally as ‘Chikungunya’, in the Newala district of Tanganyika concerns the circumstances of isolation of strains of virus, some of their properties, and their relation to the epidemic. The work, reported here, started in Newala from 18 February to 10 March, 1953, and continued thereafter in Entebbe.

The phage-typing scheme of Callow (1959) has been extended. The original number of types was 34; this has now risen to 207. Tables are presented which show the provisional type designations and the definitive designations now being introduced.

1. When refected rats are fed on adequate diet, containing vitamin B in the form of yeast, the defect in their starch-digestion disappears, and their faeces become normal.

2. Attempts to cause refection in rats receiving an adequate diet by feeding white faeces from refected rats do not influence the starch digestion of the former.

3. When refected rats, growing normally, are fed upon a diet devoid of starch (as well as of vitamin B) their body weight decreases rapidly, but in spite of this decrease they live for a considerable time.

4. Refection cannot be induced in young rats fed upon a diet devoid of starch and of vitamin B.

5. Rats may become or may remain refected when the starch of their 1. diet is replaced by dextrin containing a small amount of starch. The faeces of these rats do not seem able to refect other rats.

6. Rats may be refected without producing white faeces, but starch grains have always been present in the faeces of such rats.

7. The results of special experiments and the clinical observation of refected rats suggest an essential connection between the ability to grow and thrive without vitamin B and the defective digestion of starch.

8. Attempts at refection have no beneficial influence upon rats suffering from a deficiency of vitamin A.

9. Refection has been transmitted to albino mice receiving a diet devoid of vitamin B, but the refection lasted only for a short time. Attempts at refection of rice-fed pigeons have not succeeded.

10.The bearing of studies in refection upon several problems connected with vitamin B is discussed.

In April 2005, an outbreak of Chikungunya fever occurred on the island of Réunion in the Indian Ocean. During winter 2005, six patients developed meningoencephalitis and acute hepatitis due to Chikungunya virus. Our objectives were to determine the incidence and mortality of atypical Chikungunya viral infections and to identify risk factors for severe disease. A hospital-based surveillance system was established to collect data on atypical Chikungunya cases. Case reports, medical records and laboratory results were reviewed and analysed. We defined an atypical case as one in which a patient with laboratory-confirmed Chikungunya virus infection developed symptoms other than fever and arthralgia. We defined a severe atypical case as one which required maintenance of at least one vital function. We recorded 610 atypical cases of Chikungunya fever: 222 were severe cases, 65 affected patients died. Five hundred and forty-six cases had underlying medical conditions (of which 226 suffered from cardiovascular, 147 from neurological and 150 from respiratory disorders). Clinical features that had never been associated with Chikungunya fever were recorded, such as bullous dermatosis, pneumonia, and diabetes mellitus. Hypertension, and underlying respiratory or cardiological conditions were independent risk factors for disease severity. The overall mortality rate was 10·6% and it increased with age. This is the first time that severe cases and deaths due to Chikungunya fever have been documented. The information presented in this article may assist clinicians in identifying the disease, selecting the treatment strategy, and anticipating the course of illness.

The Preceding paper by Fridericia and his co-workers on “A Transmissible Change in the Instestinal Content, enabling Rats to Grow and Thrive without vitamin B in the Food” deals with results so novel and unexpected that a brief statement from another laboratory confirming them, is not redundant.

1. The phenomenon of refection has been confirmed.

2. The incidence of spontaneous growth of rats on a vitamin B-free diet is very much greater when potato starch instead of rice starch is used in the diet.

3. Raw arrowroot starch gave similar but not such good results.

4. The protective action is largely destroyed by gentle cooking of the starch, and less so by extraction with alcohol.

We wish to thank Prof. Sir F. G. Hopkins for his encouragement and interest during this work.

One of us (S. K. K.) is indebted to the International Health Board of the Rockefeller Foundation for a fellowship, and the other (E. W.) is indebted to the Medical Research Council for a personal grant.

Many aspects of the natural history of tuberculosis are poorly understood. Though it is recognized that clinical tuberculosis may follow shortly after initial infection (‘primary’ disease), or many years thereafter through either endogenous reactivation or after reinfection, the relative importance of these mechanisms is often disputed. The issue is complicated by the fact that the risks of developing disease are age-dependent, and reflect infection risks which may change over time.

This paper estimates the age-dependent risks of developing tuberculosis using an age-structured deterministic model of the dynamics of tuberculous infection and disease in England and Wales since 1900. The work extends the classical studies of Sutherland and colleagues. The best estimates of the risks of developing ‘primary’ disease (within 5 years of initial infection) were approximately 4%, 9% and 14% for individuals infected at ages 0–10, 15 years and over 20 years respectively, and a previous infection appeared to impart little protection against (further) reinfection, but 16–41% protection against disease subsequent to reinfection for adolescents and adults. We also provide evidence that reinfection made an important contribution to tuberculous morbidity in the past, as (i) exclusion of exogenous disease from the model considerably worsened the fit to observed notification rates, and (ii) the dramatic decline in the risk of tuberculous infection from 1950 in England and Wales accelerated the decline in morbidity among all individuals, even among the older age groups with a high prevalence of tuberculous infection. We conclude that the risk of infection is the single most important factor affecting the magnitude of the tuberculous morbidity in a population, as it determines both the age pattern of initial infection (and hence the risk of developing disease) and the risk of reinfection.

Transmission is the driving force in the dynamics of any infectious disease. A crucial element in understanding disease dynamics, therefore, is the ‘transmission term’ describing the rate at which susceptible hosts are ‘converted’ into infected hosts by their contact with infectious material. Recently, the conventional form of this term has been increasingly questioned, and new terminologies and conventions have been proposed. Here, therefore, we review the derivation of transmission terms, explain the basis of confusion, and provide clarification. The root of the problem has been a failure to include explicit consideration of the area occupied by a host population, alongside both the number of infectious hosts and their density within the population. We argue that the terms ‘density-dependent transmission’ and ‘frequency-dependent transmission’ remain valid and useful (though a ‘fuller’ transmission term for the former is identified), but that the terms ‘mass action’, ‘true mass action’ and ‘pseudo mass action’ are all unhelpful and should be dropped. Also, contrary to what has often been assumed, the distinction between homogeneous and heterogeneous mixing in a host population is orthogonal to the distinction between density- and frequency-dependent transmission modes.

For many years phage typing has proved invaluable in epidemiological studies on Salmonella typhi, S. paratyphi A and B, S. typhimurium and a few other serotypes. A phage-typing scheme for S. enteritidis is described. This scheme to date differentiates 27 types using 10 typing phages.